U.S. patent application number 13/574493 was filed with the patent office on 2012-12-06 for method for producing vinyl acetate.
This patent application is currently assigned to Wacker Chemie AG. Invention is credited to Willibald Dafinger, Mehmet Guenaltay, Peter Holl.
Application Number | 20120310007 13/574493 |
Document ID | / |
Family ID | 43923700 |
Filed Date | 2012-12-06 |
United States Patent
Application |
20120310007 |
Kind Code |
A1 |
Guenaltay; Mehmet ; et
al. |
December 6, 2012 |
Method for Producing Vinyl Acetate
Abstract
A method for producing vinyl acetate in a heterogeneously
catalyzed, continuous gas phase process by reacting ethylene with
acetic acid and oxygen in a reactor and separating the product gas
stream substantially comprising ethylene, vinyl acetate, acetic
acid, water, carbon dioxide and inert gases.
Inventors: |
Guenaltay; Mehmet;
(Emmerting, DE) ; Dafinger; Willibald; (Rohrnbach,
DE) ; Holl; Peter; (Emmerting, DE) |
Assignee: |
Wacker Chemie AG
Munich
DE
|
Family ID: |
43923700 |
Appl. No.: |
13/574493 |
Filed: |
January 14, 2011 |
PCT Filed: |
January 14, 2011 |
PCT NO: |
PCT/EP2011/050452 |
371 Date: |
August 14, 2012 |
Current U.S.
Class: |
560/261 |
Current CPC
Class: |
C07C 67/055 20130101;
C07C 67/54 20130101; C07C 67/54 20130101; C07C 67/055 20130101;
C07C 67/055 20130101; C07C 69/15 20130101; C07C 69/01 20130101;
C07C 69/01 20130101; C07C 69/15 20130101; C07C 67/54 20130101 |
Class at
Publication: |
560/261 |
International
Class: |
C07C 67/04 20060101
C07C067/04; C07C 69/01 20060101 C07C069/01 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 21, 2010 |
DE |
10 2010 001 097.9 |
Claims
1. A process for preparing vinyl acetate in a heterogeneously
catalyzed, continuous gas-phase process by reacting ethylene with
acetic acid and oxygen in a reactor and fractionating the product
gas stream containing essentially ethylene, vinyl acetate, acetic
acid, water, carbon dioxide and inert gases, by a) introducing the
product gas stream into a first distillation column (preliminary
dewatering column), b) cooling the gas mixture exiting at the top
of the first distillation column to from -20 to +50.degree. C.,
with the condensate obtained forming an aqueous phase and an
organic phase, c) taking off the aqueous phase formed in step b),
d) introducing all or part of the organic phase formed in step b)
into a collection vessel or feeding it as runback to the top of the
first distillation column in step a), e) scrubbing the gas which
has not been condensed in step b) in a scrubbing column (recycle
gas scrubber) operated using acetic acid and taking off an acetic
acid solution containing vinyl acetate at the bottom of the
scrubbing column, f) introducing the acetic acid solution
containing vinyl acetate from step e) into a second distillation
column (azeotropic column), g) introducing the bottom product from
step a) likewise into the second distillation column f), h) cooling
the overhead vapour from the second distillation column to form an
aqueous phase and an organic phase, i) taking off the aqueous phase
formed in step h), j) optionally recirculating part of the organic
phase formed in step h) as runback to the top of the second
distillation column f), k) introducing the remaining part of the
organic phase formed in step h) into the collection vessel named in
step d), l) introducing the liquid from the collection vessel named
in steps k) and d) into a third distillation column (dewatering
column), wherein m) vinyl acetate is separated off as side offtake
stream from the third distillation column of step I).
2. The process for preparing vinyl acetate according to claim 1,
wherein the organic phase formed in step b) contains from 90 to 99%
by weight of vinyl acetate, .ltoreq.2% by weight of acetaldehyde,
from 0.5 to 8% by weight of water, .ltoreq.250 ppm of ethyl acetate
and .ltoreq.250 ppm of methyl acetate, where the values in % by
weight are based on the total weight of the organic phase from step
b).
3. The process for preparing vinyl acetate according to claim 1,
wherein the organic phase formed in step h) contains from 90 to 99%
by weight of vinyl acetate, .ltoreq.2% by weight of acetaldehyde,
from 0.5 to 8% by weight of water, .ltoreq.250 ppm of ethyl acetate
and .ltoreq.250 ppm of methyl acetate, where the values in % by
weight are based on the total weight of the organic phase from step
h).
4. The process for preparing vinyl acetate according to claim 1,
wherein the organic phases collected in the collection vessel from
steps d) and k) contain .ltoreq.25 ppm of acetic acid.
5. The process for preparing vinyl acetate according to claim 1,
wherein the vinyl acetate is taken off in the form of a gas or in
liquid form from the third distillation column in step m).
6. The process for preparing vinyl acetate according to claim 1,
wherein the product separated off in step m) contains .gtoreq.99%
by weight of vinyl acetate, based on the total mass of the
product.
7. The process for preparing vinyl acetate according to claim 1,
wherein the product separated off in step m) contains .ltoreq.100
ppm of water, acetic acid, .ltoreq.300 ppm of ethyl acetate and
.ltoreq.50 ppm of aldehydes.
8. The process for preparing vinyl acetate according to claim 1,
wherein the product separated off in step m) contains .ltoreq.50
ppm of acetic acid.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is the national phase filing of
international patent application No. PCT/EP2011/050452, filed 14
Jan. 2011, and claims priority of German patent application number
10 2010 001 097.9, filed 21 Jan. 2010, the entireties of which
applications are incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The invention relates to processes for preparing vinyl
acetate in a heterogeneously catalyzed, continuous gas-phase
process by reacting ethylene with acetic acid and oxygen, in which
the work-up of the product stream obtained is more efficient.
BACKGROUND OF THE INVENTION
[0003] The preparation of vinyl acetate by reacting ethylene with
acetic acid and oxygen or oxygen-containing gases in the gas phase
over a fixed-bed catalyst has been known for a long time. The
starting materials are reacted in an exothermic reaction, generally
at a pressure of from 1 to 30 bar and at a temperature of from
130.degree. C. to 200.degree. C., in a fixed-bed tube reactor or
fluidized-bed reactor to form vinyl acetate according to the
following overall equation:
C.sub.2H.sub.4+CH.sub.3COOH+1/2
O.sub.2=>CH.sub.3COOCH.dbd.CH.sub.2+H.sub.2O
[0004] The product gas stream leaving the reactor contains vinyl
acetate together with essentially unreacted starting materials,
water and also inerts and by-products such as carbon dioxide,
acetaldehyde, methyl acetate and ethyl acetate. Inerts are
essentially nitrogen, argon, methane and ethane and are introduced
into the process as impurities in the starting materials.
[0005] To isolate pure vinyl acetate from the product gas stream,
many process variants have been proposed. In DE-A 1282014 and
[0006] DE-A 1668063, it is recommended that the product gas stream
be introduced into a first distillation column from which water and
low boilers are distilled off at the top and the bottoms are
transferred to a second distillation column from which pure vinyl
acetate is distilled off at the top. To separate methyl acetate and
ethyl acetate from mixtures with vinyl acetate, DE-A 1618240
recommends water-operated extraction processes. U.S. Pat. No.
3,692,636, U.S. Pat. No. 4,934,519 and U.S. Pat. No. 6,228,226
describe azeotropic distillations of mixtures containing vinyl
acetate, water, ethyl acetate and acetic acid.
[0007] In the process of DE-A 1768412, condensable constituents
such as vinyl acetate, acetic acid and water are condensed out from
the product gas stream and are introduced as condensates into a
first distillation column (azeotropic column) from which vinyl
acetate and water are distilled off at the top and are subsequently
subjected to a phase separation. The phase containing vinyl acetate
is introduced into a second distillation column (dewatering
column), the bottoms from which are transferred to a third
distillation column (pure vinyl acetate column) from which pure
vinyl acetate is obtained at the top. In addition to the
abovementioned process steps, the gas phase remaining after
condensation of the product gas stream is scrubbed with acetic acid
(recycle gas scrubber) in the processes of DE-A 2945913 and DE-A
2943985; the scrubbing solution obtained is introduced into the
azeotropic column.
[0008] To achieve energy-saving removal of water, DE-A 2610624
recommends introducing the product gas stream into a preliminary
dewatering column from which water and vinyl acetate are distilled
off at the top and are separated after condensation and phase
separation. The phase containing vinyl acetate obtained in this way
is recirculated to the preliminary dewatering column or introduced
together with the bottoms from the preliminary dewatering column
into a dewatering column, the bottoms from which are subjected to
further distillative purification steps to obtain pure vinyl
acetate. In the processes of EP-A 1760065, DE-A 102006038689, DE
3934614, DE 3422575 and U.S. Pat. No. 4,818,347, the
above-described preliminary dewatering column is combined with a
recycle gas scrubber operated using acetic acid, an azeotropic
column and a dewatering column and also a pure vinyl acetate
column, with the pure vinyl acetate being obtained from the top of
the latter column.
SUMMARY OF THE INVENTION
[0009] In the light of this background, it was an object of the
invention to make the processes for isolating vinyl acetate from
the product gas stream more efficient, in particular in respect of
the use of energy or plant components.
[0010] This object has surprisingly been achieved essentially by
purifying the product gas stream by means of a preliminary
dewatering column, a recycle gas scrubber operated using acetic
acid, an azeotropic column and a dewatering column, with the pure
vinyl acetate being obtained from the side offtake of the
dewatering column. In contrast to the prior art known hitherto, the
process of the invention advantageously requires no additional pure
vinyl acetate column from which the pure vinyl acetate is
conventionally distilled off at the top.
BRIEF DESCRIPTION OF THE DRAWING
[0011] FIG. 1 is a schematic flow diagram for a process according
to the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0012] The invention provides a process for preparing vinyl acetate
in a heterogeneously catalyzed, continuous gas-phase process by
reacting ethylene with acetic acid and oxygen in a reactor and
fractionating the product gas stream containing essentially
ethylene, vinyl acetate, acetic acid, water, carbon dioxide and
inert gases, by
[0013] a) introducing the product gas stream into a first
distillation column (preliminary dewatering column),
[0014] b) cooling the gas mixture exiting at the top of the first
distillation column to from -20 to +50.degree. C., with the
condensate obtained forming an aqueous phase and an organic
phase,
[0015] c) taking off the aqueous phase formed in step b),
[0016] d) introducing all or part of the organic phase formed in
step b) into a collection vessel or feeding it as runback to the
top of the first distillation column in step a),
[0017] e) scrubbing the gas which has not been condensed in step b)
in a scrubbing column (recycle gas scrubber) operated using acetic
acid and taking off an acetic acid solution containing vinyl
acetate at the bottom of the scrubbing column,
[0018] f) introducing the acetic acid solution containing vinyl
acetate from step e) into a second distillation column (azeotropic
column),
[0019] g) introducing the bottom product from step a) likewise into
the second distillation column f),
[0020] h) cooling the overhead vapour from the second distillation
column to form an aqueous phase and an organic phase,
[0021] i) taking off the aqueous phase formed in step h),
[0022] j) optionally recirculating part of the organic phase formed
in step h) as runback to the top of the second distillation column
f),
[0023] k) introducing the remaining part of the organic phase
formed in step h) into the collection vessel named in step d),
[0024] l) introducing the liquid from the collection vessel named
in steps k) and d) into a third distillation column (dewatering
column), characterized in that
[0025] m) vinyl acetate is separated off as side offtake stream
from the third distillation column of step 1).
[0026] FIG. 1 shows a simplified flow diagram for the process of
the invention.
[0027] The continuous preparation of vinyl acetate is preferably
carried out in tube reactors which are charged with a fixed-bed
catalyst. These catalysts are generally supported catalysts doped
with noble metal (salt)s and promoters, for example, bentonite
spheres doped with palladium and with gold and potassium salts. The
reactor (1) is supplied with ethylene, oxygen and acetic acid and
the reaction is carried out at a pressure of preferably from 8 to
12 bar abs. (recycle gas pressure) and a temperature of preferably
from 130 to 200.degree. C.
[0028] The product gas stream (7) leaving the reactor (1) contains
essentially vinyl acetate, ethylene, acetic acid, water, oxygen and
by-products, such as carbon dioxide and ethyl acetate, and also
inerts, such as nitrogen, argon, methane and ethane. The product
gas stream (7) is preferably introduced directly, if appropriate
after being brought to a temperature of from 115 to 130.degree. C.,
into the first distillation column (preliminary dewatering column)
(2) (step a)). The preliminary dewatering column (2) is preferably
operated under recycle gas pressure. This is advantageous for
energy reasons since the product gas stream (7) contains
considerable amounts of ethylene which can in this way be
recirculated to the reactor (1) with the smallest possible outlay
for decompression and compression. The operating temperature and
the runback of the preliminary dewatering column (2) are preferably
selected so that virtually the entire ethyl acetate in the product
gas stream (7) is collected at the bottom of the preliminary
dewatering column (2). The operating temperature at the bottom of
the preliminary dewatering column (2) is preferably from 100 to
120.degree. C.
[0029] The organic phase (9) formed in step b) usually contains
from 90 to 99% by weight, in particular from 95 to 98% by weight of
vinyl acetate, .ltoreq.3% by weight of acetaldehyde, from 0.5 to 8%
by weight, in particular from 1 to 2% by weight of water,
.ltoreq.250 ppm of ethyl acetate and .ltoreq.250 ppm of methyl
acetate, where the values in % by weight are based on the total
weight of the organic phase from step b) (9). The organic phase
from step b) (9) thus contains essentially no acetic acid, i.e.
preferably .ltoreq.15 ppm, particularly preferably .ltoreq.10 ppm
and at most preferably .ltoreq.5 ppm of acetic acid.
[0030] The gas (8) which has not been condensed in step b) consists
essentially of ethylene and CO.sub.2 and small amounts of vinyl
acetate and is freed of condensable components in the recycle gas
scrubber (3) operated using acetic acid (11) (step e)). The
operation of recycle gas scrubbers is known per se to those skilled
in the art. The recycle gas stream (12) taken off at the top of the
recycle gas scrubber (3) is generally recirculated in its entirety
or in part, optionally after purification or compression steps, as
recycle gas to the reactor (1). An acetic acid solution containing
vinyl acetate collects at the bottom of the recycle gas scrubber
(3) from which part or preferably all (13) of a stream is
introduced into a second distillation column (azeotropic column)
(4) (step f)).
[0031] In the region of the top of the azeotropic column (4), the
pressure is usually from 1.1 to 1.5 bar abs. and the temperature is
from 50 to 90.degree. C. The organic phase (14) formed in step h)
usually contains from 90 to 99% by weight, in particular from 95 to
98% by weight, of vinyl acetate, .ltoreq.3% by weight of
acetaldehyde, from 0.5 to 8% by weight, in particular from 1 to 2%
by weight, of water, .ltoreq.250 ppm of ethyl acetate and
.ltoreq.250 ppm of methyl acetate, where the values in % by weight
are based on the total weight of the organic phase from step h)
(14). The organic phase from step h) (14) thus generally contains
essentially no acetic acid, i.e. preferably .ltoreq.15 ppm,
particularly preferably 10 ppm and most preferably .ltoreq.15 ppm
of acetic acid.
[0032] A side stream (16) containing ethyl and/or methyl acetate is
usually taken off from an enrichment zone above the bottom of the
azeotropic column (4). As an alternative, ethyl acetate and/or
methyl acetate can also be taken off at the bottom (15) of the
azeotropic column (4) and distilled off in a separate distillation
column. The bottoms (15) from the azeotropic column (4) contain
essentially acetic acid and are preferably recirculated in their
entirety or in part to the recycle gas scrubber (3) in step e) as
stream (11) or, optionally after further purification, to the
reactor (1).
[0033] The organic phases (9) and (14) collected in the steps d)
and k) carried out together in the collection vessel (5) preferably
contain .ltoreq.25 ppm, particularly preferably .ltoreq.10 ppm and
most preferably .ltoreq.5 ppm, of acetic acid.
[0034] In the region of the top of the dewatering column (6) the
pressure is usually from 1.1 to 2 bar abs. and the temperature is
from 50 to 90.degree. C., in particular from 70 to 80.degree.
C.
[0035] It is important in the process of the invention that the
purified vinyl acetate is taken off in the stripping section (20)
of the dewatering column (6) preferably between the fifth and
twentieth plate above the bottom of the dewatering column (6). The
vinyl acetate can here be taken off in the form of a gas or in
liquid form from the dewatering column (6), depending on the plate
of the dewatering column at which the side offtake stream (20) is
taken off. In the form of a gas, vinyl acetate is preferably taken
off from the fifth to fifteenth plate of the dewatering column (6).
If an inhibitor is present in the distillation, the side offtake
stream of vinyl acetate (20) is preferably taken off in the form of
a gas from the dewatering column (6). Inhibitors are usually used
to avoid polymerization. Customary inhibitors are, for example,
quinones.
[0036] The product obtained in step m) preferably contains
.gtoreq.99% by weight, particularly preferably .gtoreq.99.5% by
weight and most preferably .gtoreq.99.95% by weight of vinyl
acetate, in each case based on the total mass of the product.
Furthermore, the product obtained in step m) can contain, for
example, .ltoreq.100 ppm of water, .ltoreq.50 ppm of acetic acid,
.ltoreq.300 ppm of ethyl acetate or .ltoreq.50 ppm of aldehydes,
such as acetaldehyde, as secondary components. The Hazen number is
.ltoreq.10 (determined in accordance with DIN 55945 using a
spectrophotometer). The Hazen number is a conventional measure of
the colour of transparent substances.
[0037] Acetic acid can be formed to a small extent by hydrolysis of
vinyl acetate during the distillation in the dewatering column (6).
However, it can be ensured by taking off vinyl acetate from the
side offtake (20) of the dewatering column (6) that the vinyl
acetate isolated contains essentially no acetic acid. The vinyl
acetate prepared according to the invention preferably contains
.ltoreq.50 ppm, particularly preferably .ltoreq.25 ppm and most
preferably .ltoreq.5 ppm, of acetic acid.
[0038] The vinyl acetate prepared by the process of the invention
is present in the purity required for industrial applications, and
this surprisingly despite the fact that an additional pure vinyl
acetate column from which vinyl acetate is distilled off at the top
in the prior art is not used downstream of the dewatering column as
is customary in the previous prior art. For this reason, the
process of the invention allows the distillation plant for the pure
vinyl acetate column and the associated outlays for maintenance and
operation thereof, e.g. energy and steam, to be saved compared to
the prior art. This leads to a considerable reduction in the
capital and operating costs.
[0039] The following example serves to illustrate the invention
further, without the invention being restricted in any way:
[0040] In a plant as shown in FIG. 1, an organic phase having the
following composition: 96 parts by weight of vinyl acetate, 2.4
parts by weight of acetaldehyde, 1.6 parts by weight of water and
from 250 to 300 ppm of each of ethyl acetate and methyl acetate was
collected in the collection vessel (5) in the manner and under the
conditions described above. This organic phase (17) was introduced
into the dewatering column (6). The low boilers and the water were
separated off in the enrichment section (18) and (19),
respectively. Above the bottom but below (18) and (19), a side
stream (20) was taken off. The side stream (20) comprised 99.998%
by weight of vinyl acetate and contained traces of ethyl acetate
(200 ppm), methyl acetate (150 ppm) and acetic acid (30 ppm).
[0041] The total mass flow of the bottom offtake stream (21) was
0.5% of the mass flow of the feed (17); the bottom offtake stream
was recirculated to the azeotropic distillation.
* * * * *